1. Field
The present invention relates to data communication, and more specifically to a novel and improved method and apparatus for controlling uplink transmissions of a wireless communication system to increase efficiency and improve performance.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on, for a number of users. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or some other multiple access techniques.
In a wireless communication system, communication between users is conducted through one or more base stations. A first user on one terminal communicates with a second user on a second terminal by transmitting data on the uplink to a base station. The base station receives the data and can route the data to another base station. The data is then transmitted on the downlink from the base station to the second terminal. The downlink refers to transmission from the base station to the terminal and the uplink refers to transmission from the terminal to the base station. In many systems, the uplink and the downlink are allocated separate frequencies.
In a wireless communication system, each transmitting source (e.g., terminal) acts as potential interference to other transmitting sources in the system. To combat the interference experienced by the terminals and base stations and to maintain the required level of performance, conventional TDMA and FDMA systems resort to reuse techniques whereby not all frequency bands or time slots are used in each cell. For example, a TDMA system may employ a 7-cell reuse pattern in which the total operating bandwidth, W, is divided into seven equal operating frequency bands (i.e., B=W/7) and each cell in a 7-cell cluster is assigned to one of the frequency bands. Thus, in this system every seventh cell reuses the same frequency band. With reuse, the co-channel interference levels experienced in each cell are reduced relative to that if all cells are assigned the same frequency band. However, reuse patterns of more than one cell (such as the 7-cell reuse pattern used in some conventional TDMA systems) represent inefficient use of the available resources since each cell is allocated and able to use only a fraction of the total system resources (e.g., operating bandwidth).
CDMA systems are capable of operating with a 1-cell reuse pattern (i.e., adjacent cells can use the same operating bandwidth). First-generation CDMA systems are primarily designed to carry voice data having a low data rate (e.g., 32 kbps or less). Using code division spread spectrum, the low-rate data is spread over a wide (e.g., 1.2288 MHz) bandwidth. Because of the large spreading factor, the transmitted signal can be received at a low or negative carrier-to-noise-plus-interference (C/I) level, despread into a coherent signal, and processed. Newer generation CDMA systems are designed to support many new applications (voice, packet data, video, and so on) and are capable of data transmission at high data rates (e.g., over 1 Mbps). However, to achieve the high data rates, high C/I levels are required and the need to control interference becomes more critical.
There is therefore a need in the art for techniques to control uplink transmissions to support data transmission at high data rates and achieve better utilization of the available resources.